The subject matter of the invention is a container for the long time storage of radioactive materials, especially spent fuel elements, in suitable geological formations which has cathodic protection provided by a direct current source connected to an anode.
Spent fuel elements after a temporary storage in water basins are either immediately or after a limited further intermediate storage reprocessed. Thereby, the nuclear fuel and breeded materials are separated from the fission products and again recycled to the fuel cycle. The fission products according to known processes are conditioned, for the most part using large amounts of valuable materials, as for example, lead and copper and are finally disposed of in a non-retrievable manner in suitable geological formations such as salt domes or bedded salt.
Futhermore, there has been considered (reports of the Kernforschungszentrum Karlsruhe KFK 2535 and 2650) to not reprocess the irradiated fuel elements in the foreseeable future, to give up the fuel and breeded materials in them and, after a suitable decay time in interim storages to finally dispose of the fuel elements in repositories in salt formations. The storage period of the spent fuel elements in the repository thus may last up to hundreds of years and more.
Because of the undetermined storage time, there are placed special requirements on such containers suited for long term storage and final disposal. Increasing the difficulty is the fact that the container repository must be inaccessible and, consequently, the possibilities of supervision are limited or even zero.
There are designs--partly rather expensive and sophisticated--to store the spent fuel elements or radioactive waste by means of containers made of metal or concrete in geological formations as, e.g., in dry salt formations (Report of the Kernforschungszentrum Karlsruhe KFK 3000).
However, the use of concrete is problematical since long time experience over hundreds or even over thousands of years is of course not obtainable. Metal containers, e.g., of steel, cast iron, especially spherical graphite cast iron, lead, copper, or other materials have disadvantages too. Among others, these are partially in the production costs, above all, however, in the area of corrosion, since among others water intrusions, even though there is only a slight possiblity of occurrence, must be included in safety considerations of industrial safety.
For the long term storage of spent fuel elements and other radioactive materials there have already been proposed single or multiple layer containers of various steels, in part with coatings of titanium, zirconium, or other materials, of copper or corundum. These containers, however, are either very expensive or not sufficiently resistant to corrosion. In the case of containers made of corundum, there is still a lack of production experience.
There has already been proposed (German OS No. 31 03 558 and related Holtmann U.S. application Ser No. 344,966 filed Feb. 2, 1982, the entire disclosure of the Holtmann U.S. application being incorporated by reference and relied upon) to provide the protection against corrosion of containers for the long term storage of radioactive materials by means of sacrificial anodes, in which case the anodes in the presence of an electrolyte are consumed in the course of time. It is also known to protect objects in corrosive media cathodically by connecting the object to be protected with an anode and a source of direct current.
The invention, therefore, is based on the problem of providing a container for the long term storage of radioactive materials, especially spent fuel elements, in suitable geological formations with cathodic protection by a direct current source connected with an anode, which guarantees an intact barrier for a long period of time even in case of intrusion of water or brine, without maintenance and inspection.